1. Field of the Invention
The present invention generally relates to wireless train crossing warning systems, and more specifically to a wireless train proximity alert system that provides a constant warning time signal.
2. Description of the Related Art
There are several hundred thousand railroad grade crossings exist at the intersection of railways and roads in the United States alone. It is important to provide reliable and accurate warning signals of approaching trains to prevent accidents. Many of these crossings are instrumented with the conventional "crossbuck" warning bell and light mounted pole which are very expensive to build and maintain. However, over 100,000 grade crossings have no warning system.
U.S. Pat. No. 4,942,395 discloses a "Railroad Grade Crossing Motorist Warning System" that includes a locomotive mounted transceiver for transmitting a constant and directional radio frequency beacon and a transceiver mounted at a railroad grade crossing for receiving the beacon signal and emitting an omnidirectional radio warning signal, and assumes that all vehicles will be equipped with a receiver for receiving the warning signal and activating visual and audio alarms for the driver. In this system, the train emits a signal of constant strength that attenuates as it propagates away from the train. As the train gets closer to the crossing grade the received signal strength increases until it exceeds a threshold at which time the crossing-based transceiver emits the warning signal. Similarly, as the vehicle approaches the crossing grade, the received strength of the warning signal increases until it exceeds another threshold and activates the alarm.
This approach can be inaccurate, since it doesn't account for the train's speed, the region's topography or the vehicle's speed. If the train or vehicle is traveling either very fast or very slow the alarm may be too early making it possible for the driver to forget, or too late for the driver to respond. Furthermore, tunnels or mountains can effect the signal's strength. With a beacon mounted on the locomotive and projecting a directional signal, the warning signal and alarm will be deactivated when the locomotive passes the crossing-based transceiver while the rest of the train is still passing through the crossing. Thus, approaching vehicles may not receive the warning signal and produce the alarm and may run into the side of the train. Approximately one-third of all crossing accidents involve this type of accident.
The crossing-based transceiver projects the warning signal in all directions, and can cause many false alarms in vehicles traveling away from the crossing or on non-intersecting roads. A high occurrence of false alarms is not only annoying, but dangerous because the vehicle's operator may lose confidence in the system and ignore a true alarm. If the crossing transceiver should fail, the warning signal will not be transmitted and the train will be unaware of the failure. Furthermore, when an accident does occur, it is important to be able to establish the sequence of events leading up to the accident, especially the confirmed reception of the warning signal by the vehicle. This system has no tracking capabilities.